1. Field of the Invention
The present invention relates to data storage apparatus for magnetically read and writing information on data storage media. More particularly, the invention concerns the fabrication of suspension assemblies designed to carry read/write heads in magnetic disk drive storage devices.
2. Description of the Prior Art
By way of background, a read/write head of a magnetic disk drive storage device (“disk drive”) is typically incorporated on an air bearing slider that is designed to fly closely above the surface of a spinning magnetic disk medium during drive operation. The slider is mounted at the end of a suspension assembly that in turn is cantilevered from the arm of a pivotable actuator. When energized, the actuator sweeps the suspension across the spinning disk surface, allowing the read/write head to read and write data in a series of concentric tracks.
The suspension of a conventional disk drive typically includes a relatively stiff load beam whose base end is attached to the actuator arm and whose free end mounts a flexure that carries an associated slider and its integrated read/write head in a gimbaled configuration. The load beam suspends and loads the read/write head toward the spinning disk surface and the flexure allows the read/write head to pitch and roll in order to adjust its orientation for unavoidable disk surface run out or flatness variations. These components are quite small. A typical suspension is about 11-22 mm in length. The load beam typically has a thickness of between about 0.03-0.1 mm and the flexure typically has a thickness of between about 0.02-0.03 mm. The slider is typically about 1.25 mm×1.00 mm×0.30 mm, and the read/write head carried thereon is a fraction of that size.
A design requirement of a disk drive suspension load beam is that it be compliant in the vertical bending direction (normal to the disk surface) to facilitate proper gram loading of the slider and read/write head relative to the supportive air bearing force. At the same time, the load beam must be relatively stiff in the horizontal direction (parallel to the disk surface) to prevent off-track sway misalignment. It must also be torsionally stiff to prevent off-track misalignment due to rotational displacement. In addition to these static structural requirements, the load beam must have good dynamic characteristics to prevent unwanted vibration and flutter. Excessive gain caused by resonance at critical dynamic frequencies can induce unwanted torsion, sway and bending, all of which can contribute to track misalignment problems, excessive noise, and undue wear. Dynamic design considerations have become particularly acute as recording density and TPI (Tracks Per Inch) requirements continue to increase. This has necessitated high track servo bandwidths, which in turn has established a need for higher dynamic performance suspensions.
Disk drive suspension load beams have been conventionally formed from stainless steel sheet stock that is cold rolled to its desired thickness using a rolling reduction technique. The cold rolling produces a thin load beam material with high hardness and strength, and having a substantially uniform thickness throughout its length and width. More recently, photo-chemical partial etching has been employed to form pockets of reduced thickness in the rolled material. The goal of this effort is to improve load beam dynamic characteristics by reducing weight and inertia as much as possible without sacrificing the required static and dynamic stiffness characteristics. In general, partial etching allows a load beam to perform much better than conventionally rolled load beams that have not been etched. This approach has also been found to offer a great deal of design freedom because many elaborate pocket geometries can be formed, thereby allowing dynamic characteristics to be fine-tuned by distributing load beam mass and stiffness in strategic fashion.
Notwithstanding its advantages, photo-chemical etching generates excessive tolerances in the vertical direction (e.g., 2-4 times that of rolled material). This can produce unacceptable variations in gram loading and torsional dynamic characteristics. The problem is that the tolerances required to produce satisfactory pocket depth uniformity are at the process limits of photo-chemical etching. Although the depth of material removed is substantially a linear function of the length of time the metal is exposed to the chemical etching solvent, there are a number of variables that affect the ability to precisely control the amount of metal removed. Such variables include temperature, chemical contamination, chemical solvent concentration, impurities in both solvent and metal, and initial metal thickness.
An additional problem associated with partial etching is its tendency to relieve the internal stresses that are locked into the steel material during the cold rolling reduction process. This stress relief may cause an unacceptable lowering of load beam strength in the etched areas.
Accordingly, an improved manufacturing method is needed that addresses the above-described load beam construction issues. What is particularly required is a manufacturing method that allows the advantages of load beam partial etching to be preserved while avoiding its attendant disadvantages.